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Mission Information

The four-stage Taurus XL rocket, built by Orbital Sciences Corp., is designed to be a versatile and dependable vehicle that can place a payload weighing up to 3,000 pounds into low-Earth orbit. It is a ground-launched version of the highly successful, air-launched Pegasus rocket.

You can share in the excitement of the live countdown via NASA TV or the Web. Coverage usually begins about two hours prior to liftoff. Below are some key events to watch for during a Taurus XL countdown. Keep in mind that these are only highlights, and event times and lengths may change from mission to mission.

Note: Times below begin in L-time, then changes to T-time when that clock starts. L-time is the absolute time remaining until scheduled liftoff. T-time includes built-in holds, in which the countdown clock pauses for a specified period of time.

L-3 hours, 20 minutes

Launch controllers check the communications between the control center, the range, and the launch control van near the pad

Spacecraft is verified ready for the launch countdown

L-2 hours, 50 minutes

Verify "T" clock and "L" clock are set correctly

Ensure tracking assets are ready to support the launch window

L-2 hours, 20 minutes/T-2 hours

Weather briefing

Start countdown clock at T-2 hours and counting

T-1 hour, 45 minutes

Clear launch site

T-1 hour, 25 minutes

Turn on avionics external power

Verify range is receiving closed-loop telemetry

T-1 hour, 15 minutes

Conduct telemetry and C-band tests

Conduct transient power test

Conduct avionics internal power test

T-55 minutes and holding

Built-in 15-minute hold

Launch team polled for readiness to proceed with the countdown

T-55 minutes and counting

Countdown resumes

Load navigation data into the Taurus flight computer

T-45 minutes

Weather and wind briefings

Verify flight hazard and caution areas are clear

T-25 minutes

Turn on external Flight Termination System power supply

T-20 minutes

Flight Termination System switched to internal power

T-12 minutes and holding

Built-in five-minute hold

Launch team is polled for readiness to switch spacecraft to internal power